Basically I'm considering the physiology of eyes and camouflage might look like on an eyeball planet; tidally locked to the sun so the sun is stationary in the sky. At any point on the habitable twilight-zone the sun would therefore be stationary somewhere near the horizon. The eyes might also be slightly different in the twilight-zone slightly nearer the sun-facing side than closer to the shadow-side of the planet, the sun being slightly higher in the sky or right on the horizon, respectively.

Research: The Functions of Different Pupil Shapes http://www.koryoswrites.com/nonfiction/the-functions-of-different-pupil-shapes/, Eyeball Planet https://en.wikipedia.org/wiki/Eyeball_planet, https://www.space.com/20856-alien-planets-eyeball-earths.html Camouflage https://en.wikipedia.org/wiki/Camouflage http://animals.howstuffworks.com/animal-facts/animal-camouflage.htm

The shape of the pupil doesn't seem to be directly related to the direction of light, unless there's anything I've missed. I'm looking for any good reason for slit-pupils and such rotating 90° because of the near-horizon sun, if there is any. If slit-pupils even would be as useful if the light is always the same.

Maybe some watchful grazing animals could evolve with one eye adapted for facing the sun and one for facing the shade? Something I'm considering. If anyone knows about eyes adapted to facing direct sunlight I'd love to hear it.

I've considered corpora nigra, like horses have, could be common to reduce glare; maybe positioned on the outwards side of the pupil rather than above.

I could not find any information regarding the brow ridges having to do with shading the eyes from the sun. If that is at all likely, perhaps brows ridges could evolve on the side of the eye-socket as well as above.

If anyone knows of any research regarding eyelids being horizontally over and under the eyes rather than vertically, I'd love to know that because I haven't been able to find any regarding light. It seems to mostly be about protecting the eye from dust and dryness and such, but maybe vertical eyelids could evolve if that depends on the direction of light. Let me know if you know of anything that could justify it.

Then there's the camouflage to hide from the aforementioned horizontal-light-adapted eyes.

Maybe some way to capitalize on the eyes' different physiology, ways to sneak up on something while constantly casting long shadows, sneaking up on something while facing the sun without being blinded, or being covered in patterns that take advantage of the sun consistently casting long shadows. Would stripes be the go-to pattern, or is that pattern for other reasons?

I guess regular countershading wouldn't work, unless it would be viable having the sides countershaded rather than the bottom? What colors would be best in perpetual dusk/twilight? Please share if you know! Any examples of animals that accomplish any of the above would be great!

ANY related information you have would be greatly appreciated.


1 Answer 1


Maybe some watchful grazing animals could evolve with one eye adapted for facing the sun and one for facing the shade?

I am not a biologist, so I can not provide you with an definitive answer about this. But I recently read (in [1]) about Anableps anableps, a fish, which has four pupils in two eyes. Each of his eyes is constructed with one underwater pupil and a "abovewater" pupil.The underwater pupil is adapted to the different optical properties of water. The interesting thing for you might be, that light rays of both pupils are then bent to one retina thus saving the brain from handling the input of four eyes.

So I propose, that your animal has two eyes with two pupils each. One pupil per eye is suitable for looking into the sun and one for dimmer lightning. It may close one of each pupils separately and thus be able to adapt to the current view direction of the eye.

[1] Land, M. F. and Nilsson D.-E.; Animal Eyes; Oxford Animal Biology Series; pages 118 to


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